ROTHAMSTED STUDIES OF SOIL STRUCTURE V.

Three pairs of soils were chosen, each with one difficult and one easily manageable soil with similar texture. Mechanical composition and organic matter content greatly affected the measured physical properties some of which related to the field behaviour of each pair. Soils from all horizons were stable to water slaking except some subsoils on the Ragdale, Hanslope, Salop, and Flint series. Dry and total mechanical slaking were less and breaking strengths more for the Denchworth, Evesham, Ragdale and Hanslope series than for the Salop and Flint soils. Water-holding capacity was largest for the Denchworth and Evesham soils, but slow penetration of water into their dense clods could influence regeneration of tilth.     

FURTHER STUDIES ON VARIABILITY OF SOIL CHEMICAL PROPERTIES: EFFICIENCY OF SAMPLING PROGRAMMES ON AN UNCULTIVATED BROWN EARTH

Assessments of mean and range of variation for pH, loss on ignition, total nitrogen, and exchangeable K, Na, Ca, Mg, and Mn in the surface horizon of a uniform uncultivated soil have been made by nine sampling programmes. The selected soil was known to have spatial chemical variability of magnitudes widely found in other soils and situations. The effort involved in these programmes was, for sampling and analysis time, from 1.2 to 66 man-days. The most complete sampling programme (275 samples each a composite of 10 cores), was used as a standard against which to compare the efficiency of the other programmes. Mean values for chemical quantities other than loss on ignition differed statistically significantly between programmes but there was no consistent trend with any particular programme. Knowledge of the range of variation is believed to be very important in interpretation of analyses and it is found that a programme using only 6 composite samples measures > 50 per cent of the range for most quantities and that a programme using about 25 composite samples measures at least two-thirds to three-quarters of the total range.     

Nitrogen Transformations and Decomposition in Litter and Humus from beneath Closed-Canopy Sitka Spruce

Samples of litter and humus from beneath 10 m tall, closed-canopySitka spruce planted on a brown forest soil were incubated underboth field and laboratory conditions to measure mineral nitrogenproduction and carbon dioxide evolution. Mineral nitrogen productionin enclosed samples over 12 months was equivalent to 50 and17 kg N ha^–1 in litter and humus, respectively. Applicationsof fertilizer NPK (200 kg N ha^–1 as ammonium nitrate,100 kg P ha^–1 as unground rock phosphate and 150 kg Kha^–1 as potassium chloride), 18 months previously, decreasedthese values slightly, but stimulated the production of nitratein both litter and humus. Compared with samples kept under laboratoryconditions at 10°C, those incubated in the field at a similarmean temperature released less carbon dioxide and, in the caseof fertilized humus produced smaller amounts of mineral nitrogen.     

Effect of sheep, deer and cattle dung on herbage production and soil nutrient content

A field experiment compared the effects of sheep, deer and cattle dung on pasture growth and soil nutrient status. Sheep and deer dung pellets degraded rapidly within three to eight weeks, while it was 12 months before all visible cattle dung had gone from the soil surface. The cattle dung initially reduced herbage yield owing to smothering. However, after 40 days, herbage around the edges of the dung patch responded positively to the dung and more dry matter was produced in this patch than in the control patch during the first 12 months. There was no measurable herbage response to sheep dung, but deer dung significantly increased herbage production. While the rate of nutrient application per unit area was similar for sheep and deer dung, the latter was more evenly spread within the patch area. Consequently, a greater percentage of pasture plants in the patch received nutrient additions from the deer dung and a measurable response was recorded. Twelve months after dung application, soil nitrate, phosphate and organic C were higher in dung patches than in the control patches. In cattle dung patches, this response was accompanied by higher microbial biomass C levels, arylsulphatase and arylphosphatase activities. Some residual effect on organic C levels was still evident three years after cattle dung application.     

Contribution of white clover varieties to total sward production under typical farm management

White clover varieties, potentially suitable for inclusion in seed mixtures for mixed stock-rearing farm systems, were evaluated when growing with S23 perennial ryegrass under rotational sheep grazing with a silage cut in late May or early June, as practiced on farms. Monoculture grass swards were also included to enable the direct and indirect contribution of white clover to total sward production to be evaluated.
White clover increased total sward production during all three years of the trial by an average of 50%. Although clover content of swards were similar, large differences occurred in their grass content, especially in the third year, when difference in total yields of swards based on large–leaved clover varieties was 2 t ha ⁻¹ while difference in clover yield was only 0-6 to ha^–1 The indirect contribution of white clover, namely the extra grass resulting from N transfer, was greater in the spring than in the autumn. It was also greater for Nesta than for other varieties. and exceptional for this variety in that the increase in grass yield above that of grass monoculture was maintained over three harvest years.     

Potential seed yield of white clover varieties

Fifteen varieties of white clover were sown in order to assess the seed yielding ability of new and potential varieties and to examine those plant factors which affect seed yield. Counts were made on number of inflorescences m^-2, proportion of ripe inflorescences and other inflorescence and seed characters. The data were used to compute potential seed yields.
Average potential seed yields were 276 and 76 kg ha^-1 in the first and second year, respectively. The decrease in the second year seed yields underlines the overriding effect of adverse weather conditions during the critical June to August period. The major effect was a reduction in the number of inflorescences produced, the number of florets per inflorescence and seeds per floret.
Some of the new listed varieties have a significantly higher seed potential than SI00, e.g. Menna (+ 38%) and Olwen (+28%), and this should facilitate the production of adequate seed supplies of British bred varieties.     

Effects of altitude on circadian rhythm of adult locomotor activity in Himalayan strains of Drosophila helvetica

Background  

We recently reported that the altitude of origin altered the photic and thermal sensitivity of the circadian pacemaker controlling eclosion and oviposition rhythms of high altitude Himalayan strains of Drosophila ananassae. The present study was aimed at investigating the effects of altitude of origin on the pacemaker controlling the adult locomotor activity rhythm of D. helvetica.     

A comparison of grass/white clover and grass silages offered to dairy cows as the sole feed

Two diets were compared: perennial ryegrass ( Lolium perenne L.) silage and perennial ryegrass/white clover ( Trifolium repens L.) silage, in each case fed ad libitum , without supplementation, to lactating dairy cows. The comparison was made with silages cut on each of four dates. The crops were wilted to a dry matter content of at least 256g kg^-1 and no additives were used.
The grass/clover silages were well preserved at all four cuts. The grass was well preserved at three cuts, but, at a May cut, the grass silage was less well preserved and less digestible than the grass/clover silage. When the May silages were fed, milk yield was higher with grass/clover than with grass. Taking the experiment as a whole, however, milk yield and composition were similar on the two diets. The grass/clover silages had a lower proportion of cell wall and their intake by dairy cows was consistently higher than that of the grass silages.
It is concluded that perennial ryegrass/white clover crops can be ensiled successfully and fed successfully, with high intake, to lactating dairy cows, but it should not be assumed that cows will give more milk than when fed equivalent all-grass silage.